A FIR GRATING POLYCHROMATOR USING CONICAL DIFFRACTION AS A DIAGNOSTIC TOOL FOR ECE PLASMA MEASUREMENTS
A new 6(12) grating polychromator based on the principle of conical diffraction has been designed for the millimetre wavelength range. The application will be the study of electron cyclotron emission spectra of large tokamaks. The conical diffraction principle has two relevant advantages, namely a wavelength independent efficiency and a very large wavelength range, accessible by one grating, 85-425 GHz. The experimental dispersion and imaging characteristics are shown. The resolution of the instrument is shown to depend linearly on lambda, which combined with the typical 1/R dependence of the tokamak magnetic field gives almost constant spatial resolution in the line of sight. The spectral range of the instrument (DELTAlambda = 0.33 mm independent of grating angle) results in a spatial coverage of the plasma in second harmonic radiation of DELTAd - d=0.03 B-omicron-epsilon, where d is the diameter of the plasma, B-omicron the magnetic field on axis and epsilon the inverse aspect ratio, R/a. The radiation is detected by cryogenically cooled InSb, with about 1 mu temporal resolution. The theoretical efficiency is given.
Bibliographic Reference: INFRARED PHYSICS, VOL. 24 (1984), NO. 6, PP. 511-525
Record Number: 1989123072700 / Last updated on: 1987-01-01
Available languages: en